1. Field of the Invention
The present invention relates to a display device and a semiconductor device, and more particularly to a hold-type display device such as a liquid crystal display device. The present invention especially relates to a method for driving a liquid crystal display device in which peak luminance is controlled. Further, the present invention relates to an electronic device including such a display device for a display portion.
2. Description of the Related Art
A liquid crystal display device has advantages such as small thickness, lightness in weight, and low power consumption as compared to a display device using a cathode-ray tube (CRT). Further, since a liquid crystal display device can be applied to a wide range of display devices from a small display device including a display portion with a few inches diagonal to a large display device including one with a diagonal of more than 100 inches, the liquid crystal display device is widely used as a display device of a variety of electronic devices such as a mobile phone, a still camera, a video camera, and a television receiver.
Although thin display devices including liquid crystal display devices are starting to widely spread in recent years, measures to improve the image quality still have been taken because the image quality is not always satisfactory. For example, as problems of the image quality of the liquid crystal display device, the contrast ratio is reduced by faint light emission at the time of black display, and a hold-type display device (or a hold-driving display device) causes afterimages and thus the moving image quality is reduced, for example. Note that a hold-type display device is a display device in which luminance is kept for one frame period with little change. A display device such as a CRT, in which display is performed by light emission that lasts only for an extremely short time in one frame period, is referred to as an impulse-type display device (or an impulse-driving display device) in contrast to the hold-type display device.
It has been found that a peak luminance control method is one technical factor in improving the quality of images displayed on a display device. The peak luminance is luminance in a region (a high gray level region) which is part of a screen when an image having high gray level data only for the part of the screen (an image with high peak gray level) is displayed. By increasing the peak luminance depending on the area of a high gray level region or the like, the capability of expressing brightness of night view, sparks, luster of metal, and the like can be greatly improved, and the quality of images to be displayed can be improved.
In a display device using a CRT, luminance of only part of an image can be easily made higher, and thus, the capability of expressing an image with high peak gray level is high. Techniques to realize such display in a liquid crystal display device are disclosed in Patent Documents 1 and 2, for example.